The field of this invention is that of electrical heaters and the invention relates more particularly to self-regulating heaters having electrical resistance heater elements of a ceramic material of positive temperature coefficient of resistivity and to early fuel evaporation systems for automotive engines using such heaters.
Conventional early fuel evaporation (EFE) systems for automotive engines incorporate electrical heaters for heating the air-fuel mixture passing to the engine during the engine warm-up period, thereby to enhance fuel evaporation on a cold day to assure smooth engine starting or to reduce exhaust pollution emissions. The heaters usually incorporate electrical resistance heater elements of a thin disc shape formed of a ceramic material or positive temperature coefficient of resistivity and the ceramic material is usually adapted to display a sharp increase in resistance when the heater self-heats above a particular transition temperature. The transition temperature is usually on the order of 80.degree.-180.degree. C. and is characteristic of the selected ceramic material. Such heater elements are self-regulating in that they display progressively increasing resistance and reduced heat output as the heater temperature increases until the heater temperature stabilizes at the level where the reduced rate of heat output from the element is balanced by the rate of heat dissipation from the element.
In certain well known EFE systems, the heater includes a metal radiator having one heat-transferring side provided with heat-distributing rods or fins. The heater is mounted in an automotive fuel supply system so that the heat-transferring side of the radiator is disposed in heat-transfer relation to the air-fuel mixture being passed through the system to the engine. Typically, the heater is mounted in the intake manifold of the engine beneath the air-fuel supply passage of the carburetor so that any unvaporized fuel droplets which enter the intake manifold tend to fall on the heat-transferring side of the radiator and so that the air-fuel mixture fed into the intake manifold from the carburetor passes over the rods or fins on the radiator. In that known type of heater device, the thin ceramic heater disc elements are located on an opposite, heat-receiving side of the radiator member so that the heat generated by the elements is transmitted through the metal radiator member to heat the air-fuel mixture passing through the intake manifold. Usually, one flat side of each of the thin ceramic heater discs is secured in electrically and thermally conducting relation to the heat-receiving side of the radiator and the radiator is connected to electrical ground. Electrical terminal means then engage the respective opposite sides of the heater discs for electrically connecting the resistance heater elements in parallel relation to each other. In that arrangement, the heaters are conveniently energized from the battery or generator power source of the automotive engine when the engine is started by closing of the ignition switch and are adapted to provide a desired heating effect to the air-fuel mixture during cold weather to achieve smooth engine performance during start up. The heating effect also serves to reduce emission of pollutants such as unburned hydrocarbons from the engine exhaust.
However, it is found that the noted heaters impose a significant load on the power supply capacity of the automotive engine during the engine start-up period. This is particularly true in that provision has to be made to reserve a sufficient part of the power supply capacity to meet the peak current demand by the heaters when they are in their high current mode as initial engine starting occurs while also adapting the power supply system to meet the needs of many other electrically-operated automobile components.
It is an object of this invention to provide a novel and improved self-regulating heater device; to provide such a heater device which is particularly adapted for use in an early fuel evaporation system for an automotive engine; to provide such a heater device which is adapted to provide a desired heating effect with reduced peak current demand characteristics; and to provide a novel and improved fuel supply system for an automotive engine utilizing such a heater device.